Vegetable oil refining processes generally involve several steps including a degumming step which adds water to crude oil followed by heating and agitating the oil mixture for a period of time (e.g., 10-30 minutes) and at temperatures of typically 50 to 70° C. This mixture of hot oil and water is subjected to centrifugation wherein the water and oil are separated. In the process the hydrated phospholipids are separated with the water. The resulting partially degummed oil typically contains a quantity of phospholipids, including all the non-hydrated phospholipids. This quantity often contains the equivalent of 10 to 120 ppm of phosphorus; however, this quantity varies depending upon the precise degumming techniques and conditions used.
The partially degummed oil produced in accordance with the above process may be further degummed to remove the non-hydratable phospholipids by the addition of certain chemicals, such as phosphoric acid or base, and water and by again heating and agitating the mixture followed by centrifuging. The degummed oil produced from this step generally contains a quantity of phospholipids equivalent to 5 to 10 ppm of phosphorus.
Further improvements in degumming vegetable oils have been sought and, in particular, with regard to removing excess chemicals and further reducing the quantities of phospholipids and other impurities in the oil by using high shear mixing and cavitation.
A method disclosed in U.S. Pat. No. 4,240,972 includes adding an acid to a heated stream of crude vegetable oil and then immediately passing the mixture through a static mixer to produce an acid-in-oil dispersion having acid droplets smaller than 10 microns, and then separating the dispersion into an oil phase and an aqueous phase containing the phosphatides. This method claims that producing ultrafine acid droplets eliminates the need for lengthy acid-oil contact times and produces oil having a phosphorous level in range of 2 to 9 ppm.
U.S. Pat. No. 4,698,185 describes a vegetable oil refining method that includes the steps of finely dispersing an aqueous organic acid in a water-degummed oil to form an acid-in-oil dispersion, allowing the phases to remain in contact for a time sufficient to decompose metal salts of phosphatidic acid, adding a base to the acid-in-oil dispersion to increase pH to above 2.5 without substantial formation of soap, and finally separating the dispersion into an oil phase and an aqueous phase containing the hydrated phosphatides. The method typically utilizes 0.4 to 2 percent by weight of a 20 to 60 percent by weight organic acid solution and discloses a dispersion of at least 10 million droplets of aqueous acid per gram of oil. This refining method produces oil having a phosphorous level in range of 2 to 8.2 ppm.
U.S. Pat. No. 6,001,640 discloses oil degumming methods that use high-shear mixing. This degumming method produces oil having a phosphorous level in range 4.2 to 5.4 ppm. In another method, phospholipids can be removed from soybean oil by applying ultrasound cavitation and a small amount of degumming agent (Moulton, K. J., Mounts, T. L., “Continuous ultrasonic degumming of crude soybean oil”, Journal of the American Oil Chemists' Society, 67, 1990, 33-38). This degumming method produces oil having a phosphorous level in range of 7 to 12 ppm.
Methods disclosed in U.S. Pat. Nos. 8,911,808 and 8,945,644 and U.S. Pat. App. Nos. 2014/0087042 and 2015/0057460 involve mixing vegetable oil with degumming agents, such as water or acid, and passing the mixture through a flow-through, hydrodynamic cavitation apparatus. The method generates cavitational features in the mixed fluid such that the impurities are directly transferred from the oil phase to the water phase during cavitation conditions. It was further disclosed that the concentration of phosphorus dropped to range of 2 to 10 ppm.
A disadvantage of these cavitational methods is that a mass transfer of impurities from the oil phase to the water takes place under the influence of cavitational features (i.e. formation and collapse of bubbles) and requires a long treatment cycle. Longer residence time in the collapsing cavitation bubbles can have an impact on the structural and functional components in the vegetable oils up to the point of lipid oxidation and deterioration due to hot spots attributed by cavitation. Oil produced from these degumming methods can be useful as a food product but still contains phospholipids, for example, equivalent to at least 2 to 10 ppm of phosphorus. No degumming process for vegetables oil is known which consistently delivers oil with less than 1 to 2 ppm of phosphorus. Accordingly, there is a continuing need for alternative refining methods, which can provide cost-effective removal of phosphorous below known achieved ranges and eliminate the disadvantages resulting from mass transfer in the cavitation bubble field.